netdev - Re: [PATCH v6 net-next 0/8] net: dsa: felix: psfp support on vsc9959

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Date:   Fri, 1 Oct 2021 15:59:36 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     Xiaoliang Yang <xiaoliang.yang_1@....com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "allan.nielsen@...rochip.com" <allan.nielsen@...rochip.com>,
        "joergen.andreasen@...rochip.com" <joergen.andreasen@...rochip.com>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        "vinicius.gomes@...el.com" <vinicius.gomes@...el.com>,
        "jiri@...lanox.com" <jiri@...lanox.com>,
        "idosch@...lanox.com" <idosch@...lanox.com>,
        "alexandre.belloni@...tlin.com" <alexandre.belloni@...tlin.com>,
        Po Liu <po.liu@....com>, Leo Li <leoyang.li@....com>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "vivien.didelot@...il.com" <vivien.didelot@...il.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "horatiu.vultur@...rochip.com" <horatiu.vultur@...rochip.com>
Subject: Re: [PATCH v6 net-next 0/8] net: dsa: felix: psfp support on
 vsc9959

On Fri, 1 Oct 2021 22:46:34 +0000 Vladimir Oltean wrote:
> On Fri, Oct 01, 2021 at 03:11:15PM -0700, Jakub Kicinski wrote:
> > On Thu, 30 Sep 2021 15:59:40 +0800 Xiaoliang Yang wrote:  
> > > VSC9959 hardware supports Per-Stream Filtering and Policing(PSFP).
> > > This patch series add PSFP support on tc flower offload of ocelot
> > > driver. Use chain 30000 to distinguish PSFP from VCAP blocks. Add gate
> > > and police set to support PSFP in VSC9959 driver.  
> >
> > Vladimir, any comments?  
> 
> Sorry, I was intending to try out the patches and get an overall feel
> from there, but I had an incredibly busy week and simply didn't have time.
> If it's okay to wait a bit more I will do that tomorrow.

Take your time, I'll mark it as Deferred for now.

> In general I feel that the most glaring issue Xiaoliang has still
> avoided to address is the one discussed here:
> https://patchwork.kernel.org/project/netdevbpf/patch/20210831034536.17497-6-xiaoliang.yang_1@nxp.com/#24416737
> where basically some tc filters depend on some bridge fdb entries, and
> there's no way to prevent the bridge from deleting the fdb entries which
> would in turn break the tc filters, but also no way of removing the tc
> filters when the bridge fdb entries disappear.
> The hardware design is poor, no two ways around that, but arguably it's
> a tricky issue to handle in software too, the bridge simply doesn't give
> switchdev drivers a chance to veto an fdb removal, and I've no idea what
> changing that would even mean. So I can understand why Xiaoliang is
> avoiding it.
> That's why I wanted to run the patches too, first I feel that we should
> provide a selftest for the feature, and that is absent from this patch
> series, and second I would like to see how broken can the driver state
> end up being if we just leave tc filters around which are just inactive
> in the absence of a bridge, or a bridge fdb entry. I simply don't know
> that right now.
> It's almost as if we would be better off stealing some hardware FDB
> entries from the bridge and reserving them for the tc filter, and not
> depending on the bridge driver at all.

Maybe I shouldn't comment based on the snippets of understanding but
"steal some FDB entries" would be my first reaction. Xiaoliang said:

	The PSFP gate and police action are set on ingress port, and
	"tc-filter" has no parameter to set the forward port for the
	filtered stream.

which seems to undersell TC.